Thanos is not in Thor: The Dark World. He is not going to kill Odin. And there definitely is not going to be a Thor/Thanos fight in that movie. You might want to read up on what's known about the movie, which is already in production, before commenting on it.

I doubt we'll see Thanos vs. Odin and/or Thor in TDW, but don't bet against Thanos having a presence in the movie. Not the centerpiece, mind you, but the movie should literally open with them addressing who Loki consorted with, and how and why, and the fact that this kingpin of the Gangstas of the Nine Realms has promised to come gunning for the Lokester now that he failed to deliver the Tesseract, as was contracted.